An image sensor is a semiconductor device for converting optical images into electric signals. Image sensors may be classified into charge coupled device (CCD) image sensors and complementary metal oxide silicon (CMOS) image sensors (CIS).
A CIS generally includes a photodiode and a MOS transistor within each unit pixel, and obtains an image by sequentially detecting electrical signals of unit pixels in a switching manner.
During the fabrication method of a CMOS image sensor in accordance with the related art, a process for forming a photodiode is followed by a chemical mechanical polishing (CMP) process for forming a multilayer structure including two or more metal interconnections and a dielectric.
However, the related art method may cause a decrease in photosensitivity due to an increase in the distance between a photodiode and a color filter, and result in an increase in bad pixels due to an increase in defects.